This invention relates to a transmission mechanism and a control apparatus therefor and, more particularly, to a control apparatus for a transmission having a power transmission assembly for transmitting power from an engine, a first power train coupled to the power transmission assembly and having at least two different speed-change ratios, and a separate second power train communicating with the first power train and including a dog clutch for cutting off or switching over power.
A transmission of the foregoing type known in the art makes use of a hydraulic power transmission unit (e.g., a torque converter) as the power transmission assembly, a gear ratio transmission element, which includes a planetary gear set or sets, as the first power train, and a dog clutch-type power distributing unit (e.g., a transfer assembly for four-wheel drive vehicles, or a power take-off assembly for specialized vehicles) as the second power train. Recently, attempts have been made to automate transmission control in such transmissions, particularly those having the transfer assembly for four-wheel drive vehicles. By way of example, it has been attempted to change over the transfer section by switching gears and to effect a speed change by an automatic transmission having a planetary gear. However, with a transmission of this type, when the shaft position is in the N (neutral) range, the output shaft rotates owing to a dragging torque developed by, e.g., a clutch in the automatic transmission even though it is attempted to change over the transfer section. As a result, changing-over the transfer section becomes sluggish and it is difficult to the transfer assembly (dog clutch) in mesh.